The present invention relates to gas blast switches of the puffer type.
German Offenlegungsschrift [Laid-Open Application] No. 2,627,948 discloses a gas blast switch of this type in which the predominant portion of the electric arc cloud, the plasma, is conveyed out of an insulating nozzle into a space between the insulating nozzle and a solid countercontact of the switching path. Due to the lower energy of electric arcs in such environment compared to that in air, it is possible with this simple quenching arrangement to handle currents of up to about 63 kA at voltages of 140 kV per switching path. When higher currents are to be switched off, the plasma disposed in the space between the insulating nozzle and the countercontact acts in such a manner that high value transient voltages can no longer be supported because the presence of the plasma between the conductive faces of the movable parts of the switching path gas compressor and the stationary contact piece of the switching path provides an opportunity for flashover or re-ignition, that means after extinguishing the arc, it may happen that the arc re-ignites, for example, owing to a great slope of the building-up voltage of the switching path. In the following, this phenomenon is called flashover.
Although it has been attempted, with the structure disclosed in the above mentioned Offenlegungsschrift, to realize a certain shielding of these parts by a plasma rejecting outer shape of the insulating nozzle and by the provision of insulating members at the cylinder of the switching path compressor and at the contact pieces, such shielding is not complete enough because it is able to shield only a few parts to a certain degree. Moreover, such a structure becomes relatively expensive, particularly since it includes spring tensioned insulating members.